fix(network): retry connection-lost requests only for idempotent methods - #446

Summary

CustomHTTPProtocol silently re-issues the original request on cfurlErrorNetworkConnectionLost when no data was received — for any HTTP method. Re-issuing non-idempotent requests (POST/PUT/PATCH/DELETE) can duplicate server-side effects: a payment/order POST whose connection drops after reaching the server gets sent twice, and the app never sees the first attempt. Apple's URL loading system deliberately never auto-retries POST on connection-lost for this reason.

This limits the silent retry to idempotent methods (GET/HEAD/OPTIONS/TRACE).

Type of change

• Fix
• Feature
• Refactor
• Docs
• CI/CD

Test plan

• Unit tests updated
• Manual testing completed
• CI passing

Manual test steps

1. Intercept a POST with DebugSwift enabled and kill the connection mid-flight (Network Link Conditioner / proxy) so the task fails with networkConnectionLost before any data arrives.
2. Before: the request is transparently re-sent (server receives it twice). After: the failure is delivered to the caller, no re-issue.
3. Repeat with GET — retry still happens as before.

Checklist

• I reviewed my own changes
• I updated docs when needed
• I considered backward compatibility